The present invention relates to a process for laying a strip continuously on a profile which is generally toroidal in shape.
These days, continuous strip laying is widespread in the tyre industry and various processes have been described for depositing rubber strips or cord plies in the radial or circumferential direction.
More particularly, the field of the invention relates to laying a strip continuously in the circumferential direction on the toroidal surface of a tyre casing, where the width of the strip is very much less than the width of the receiving surface and where, moreover, the thickness of the strip is very much less than its width.
The processes suitable for performing these functions have been known for a long time and are described, by way of example, in patent nos. U.S. Pat. Nos. 3,251,722, 4,240,863 and 4,775,733 or, in a more recent version of the prior art, in U.S. Pat. No. 5,335,415.
These apparatuses are generally composed of:                a frame allowing support and rotation of the surface to be covered,        a module supplying a strip of calibrated size; this strip may equally well come from a reel on which it has been wound beforehand or, more generally, directly from a calender or an extruder incorporated in the installation,        a head for applying the strip to the receiving surface, cooperating with the above-described module and having the function of depositing the strip tangentially on said rotating receiving surface,        an automatic control device for the relative displacements of the application head relative to the receiving surface to be covered.        
The arrangement of these various modules varies from one solution to another, depending on whether the application head is moved around the laying surface or whether the laying surface is displaced relative to a stationary application head. The automatic control device in turn varies from entirely mechanical solutions to solutions making extensive use of electronics and computing to control positioning motors controlling the respective movements of the application head or of the frame supporting the tyre or alternatively rotational drive of the tyre.
However, all these solutions are characterised in that the automatic control devices make extensive use of templates, in the case of mechanical or electromechanical solutions, or of calculation algorithms founded on precise, preestablished knowledge of the shape and position of the transverse profile of the receiving surface. For each full rotation of the laying surface, the transverse pitch of the movement of the application head relative to the receiving surface is predetermined as a function of the width of the strip and the position of the application head relative to a given sector of the transverse profile of the receiving surface. These solutions are generally very suitable when the receiving surface has a known, controlled geometry, which is generally the case when a rigid shape or core is used, and also when it is necessary to deposit a quantity of rubber or cord in accordance with a particular transverse profile. The latter application is achieved by appropriately adapting the transverse pitch of the movement of the application head relative to the receiving surface so as to superpose and juxtapose the strips relative to one another in controlled and variable manner.
However, there are situations in which these devices may be considered too cumbersome to use or unsuitable.
A situation of this type arises with regard to the process of retreading tyre casings, during which it is necessary to deposit a thin layer of rubber known as bonding rubber on the outer surface of a tyre during retreading so as to reinforce the interface between the carcass and the tread. Situated at the heart of the tyre, these rubbers have the special features of being very reactive and of exhibiting very short curing times in order to minimise heat transfer when effecting vulcanisation of the carcass, in a press or autoclave, once it has been covered with its tread. This is the case in particular when rubbers known as self-curing rubbers and precured treads are used.
Under these conditions, there is no longer any question of using bonding rubbers in the form of precalendered rubber strips of the width of the receiving surface and laid as required on the latter, prior to laying of the tread, because the properties of the bonding rubber change too quickly, thus creating pressures in the organisation of the manufacturing process due to the need to limit storage and waiting times.
An elegant solution consists in depositing a bonding rubber strip coming directly from an extruder or a suitable calender in successive windings of contiguous turns, and in directly thereafter depositing the strip on the receiving surface.
In order to make use of this process entirely satisfactory, it is also advisable to remove one last obstacle consisting in the fact that tyres in the course of retreading have receiving surfaces whose transverse profiles may exhibit shapes which vary considerably from one size to another, but also within one and the same size. If it were wished to use one of the processes such as described in the prior art, it would be necessary to develop as many control formulae or algorithms for the movements of the application head as there were particular sizes and shapes of the strip receiving surface, which could entail not inconsiderable costs.
The invention such as described below has as its object the removal of the latter difficulty and proposes an apparatus allowing deposition of a strip on a rotating surface having any shape without its being necessary beforehand to determine a formula for controlling the movements of the application head.